This invention relates generally to elastic motors. More specifically, this invention relates to an improved elastic motor having a torque output that is substantially constant when averaged over time.
Elastic motors have been employed for centuries and have found particular application in model airplanes for over 150 years.
Typical prior art elastic motors, such as those used in a model airplane, generally comprise a rubber loop threaded through a hook on a propeller shaft and is further attached to another hook at the tail of the craft. As the motor is wound up it first twists the elastic into a skein, then a row of knots form and spread along the whole length. A third stage occurs when a row of knots forms in the already knotted skein. When this row is complete the rubber is substantially stretched to its limit.
Upon release of propeller, there is a burst of power. When this is spent, a period of slowly declining torque follows for the majority of the motor run and is followed by a decline to zero torque.
The torque characteristics of the prior art elastic motor devices, like those described above, make model airplane design a considerable challenge. Clearly, this is because it is difficult for a designer to properly construct design constraints when the source of propulsion has such wavering torque characteristics. Aside from model airplane design, conventional elastic motors have undesirable performance in other applications as well. The knotting of the rubber introduces internal friction in the wound skein that can be eased somewhat by lubrication. Lubrication, however, drastically reduces the useful life of the rubber.
Therefore, the shortcomings of the prior art suggest a strong need for an elastic motor design that has a constant torque characteristic and does not damage the elastic material.
The present invention is directed towards an elastic motor, more specifically, to an elastic motor having a time-averaged constant torque characteristic.
The motor system of an embodiment of the present invention starts with a reel which is wound with elastic stretched to its maximum tension. Each unit length of the elastic is allowed to relax back to its normal state while generating torque in a process that continues until the reel is fully unwound. The process may be seen as analogous to a steam engine which has a supply of steam at constant pressure. Portions of steam are fed to a cylinder where they expand to generate work (pressure times change in volume) by pushing a cylinder back to turn a wheel. When the expansion is complete the steam is exhausted and the process repeated. In the case of the present invention, a unit length of stretched elastic is connected into a system and allowed to contract to its unstressed state while turning a wheel and developing work. When fully contracted the relaxed elastic is fed to a take up reel and a new unit length of stretched elastic is taken. The process is continued until all the stretched elastic is used up. There is no twisting or knotting of the elastic and no need to lubricate it to prevent binding and wear as in a twisted skein, although some lubrication may assist operation. Thus, the present invention can be further analogized to a two-cycle gasoline engine whose pulses of torque are smoothed by a flywheel to create a constant output.
Hence, it is an object of the invention to provide an improved elastic motor.
Furthermore, it is an object of the invention to provide an improved elastic motor having a constant torque characteristic.
Further, it is an object of the invention to provide an improved means of powering portable devices.
Additionally, it is an object of the invention to provide an elastic motor having increased elastic material life.
Further, it is an object of the invention to provide an improved means of driving a dynamo.
Furthermore, it is an object of the invention to provide an improved means of powering wind-up toys and devices.
These and other objects will become apparent to those skilled in the art upon study of the following drawings and detailed description.